SU972158A1 - Method of producing vacuum in receiver - Google Patents

Description

(54) METHOD FOR OBTAINING A VACUUM IN A RECIPIENT AND A DEVICE FOR ITS IMPLEMENTATION

one

The invention relates to vacuum technology, namely to methods for cyclically producing a clean, oil-free vacuum using cryogenic condensing pumps.

A known method of obtaining vacuum in the recipient by condensation of the pumped gas on the cooled low-temperature surface 1.

The disadvantage of the known method is the high consumption of the cryoagent (liquid helium) during condensation, which is approximately 140 l / m of the pumped gas. This is due to the fact that when the low-temperature pumping surface is cooled, only the heat of evaporation of the liquid gel (5 cal / g) is used, and the cold enclosed in the vapor of the latter (53 cal / g at 4.2-42 K) is not used.

There is also known a method of obtaining vacuum in the recipient by condensing the pumped gas on low-temperature and high-temperature surfaces, cooled respectively by a liquid cryoagent and its vapors. When pumping a part of the gas, liquid helium evaporates on the low-temperature surface, the vapors of which then

They are used to condense the main mass of gas on the high-temperature surface, which allows reducing the consumption of the cryogenic agent by about an order of magnitude.

However, this method is characterized by the impossibility of its re-implementation with the above efficiency, for example, when cyclically obtaining a vacuum in the recipient. This is due to the fact that high efficiency with the method is achieved for

10 by limiting the amount of liquid gel supplied to cool the low-temperature surface from an external source of the cryogenic agent (Dewar vessel). This can be realized only in the first cycle of obtaining a vacuum in the recipient. AT

For the next 15 cycles, the low-temperature surface will be cooled by a large amount of the previously accumulated cryogenic agent, which does not allow the amount of the latter to be controlled. This leads to a corresponding increase in the flow rate of liquid gels.

Claims (2)

A device for accomplishing the above is known, a method comprising a body and a vessel with a low-temperature surface and a coil with a high-temperature surface located therein. This design of the device reduces the flow rate of liquid helium to an order of magnitude compared with known cryopumps, which use only the heat of evaporation of the cryoagent for condensation of the pumped gas (for liquid helium, equal to 5 cal / ton). This is due to the fact that in a cryopump the cryogenic vessel is cooled with liquid helium supplied from an external source of the cryogenic agent (Dewar vessel), and the coil is only cooled during the pre-cooling of the vessel from the initial to the operating temperature and during condensation on the surface of the vessel portion of the pumped gas. In this case, the coil receives the main heat load from the condensed gas (70-95%) 2. A disadvantage of the known device is the impossibility of cycling the recipient with a low flow rate of the cryoagent without removing the latter from the cryoagent container before the recipient’s next pumping cycle is removed. the turn is associated with the unproductive losses of the cryoagent. The purpose of the invention is to increase the efficiency with cyclical vacuum in the recipient. This goal is achieved by separating the pumped gas before condensation into two streams, one of which is condensed on a low-temperature surface and the other on a high-temperature one, the flow ratio being determined from the following inequality: GLi / Q-2 GI / CP (T -TO) where HH is the heat of evaporation of the refrigerant; That is the boiling point of the refrigerant, T is the current maximum temperature of the high-temperature surface; Cp is the heat capacity of the refrigerant vapor. A device for implementing the method is provided with a sealed chamber placed inside the vessel, and the coil is located with a gap relative to the inner surface of the chamber and forms a closed cavity connected through a locking and regulating device to the chamber and using a vacuum line to the recipient. The drawing shows a device for implementing the method. The apparatus for producing a vacuum comprises a housing 1 and a vessel 2 with a low-temperature surface and a coil 3 with a high-temperature surface placed therein. The device is also provided with an airtight chamber 4 placed inside the vessel 2. The coil 3 is located with a gap relative to the inner surface of the chamber 4 and forms a closed cavity 5 connected through a locking and regulating device 6 to the chamber 4 and using a vacuum line 7 to the recipient. The cavity 5 is connected to the chamber 4 by an opening 8. For connection to the recipient, the housing 1 is provided with a forevacuum 9 and a high-vacuum 10 valve. The locking and regulating device 6 is equipped with a control mechanism 11. A thermometer 12 is placed at the output of the coil 3. The method is carried out as follows. After pumping out the cavity of the housing 1, the tank is filled with liquid nitrogen. Then, liquid helium is supplied from the external source of the refrigerant to the vessel 2, before this it is necessary to connect the output of the coil 3 to the gas-holder. During pre-cooling of the vessel 2 and the sealed chamber 4, a significant amount of liquid helium is evaporated. This amount of gels, converted into steam, is enough not only to pre-cool the coil 3, but also to condense a portion of the gas pumped out from the recipient. For this, using the locking control device 7, close the opening 8 and open the valve 9. The gas coming from the recipient will then condense on the outer surface of the coil 3 (first into the liquid phase, then into the solid). After cooling the vessel 2 and the sealed chamber 4 to 4.2 K and the beginning of accumulation of the refrigerant in the vessel 2, intensive evaporation of the liquid helium stops, as can be seen from the readings of the thermometer 12 installed at the outlet of the coil 3 and showing the temperature of the helium vapor vapor, also to reduce the speed of pumping gas from the recipient. Using the control mechanism 11 (manually or automatically), the locking-regulating device 7 is set in such a position that the flow of pumped gas passes through the opening 8, for example Qi 10 l / s, which condenses on the inner surface of the sealed chamber 4 (washed from the outside liquid helium) together with parasitic heat supply to vessel 2 evaporates liquid helium in vessel 2 in an amount sufficient to condense on the surface of the coil cooled only by helium vapor the flow of pumped gas Q2 190 l / s. Thus, the inner surface of the sealed chamber 4 is also a low-temperature surface, and the outer surface of the coil 3 is a high-temperature surface. During the cryopump operation, the temperature of the low-temperature surface is constant and determined by the type of refrigerant used (4.2 K for liquid helium), while the temperature of the high-temperature surface is variable and is determined by both the type of pumped gas and its pressure at the time of pumping. When pumping nitrogen, it varies from 77.4 K (at 760 Torr) to 34 K (at SW Torr) and below. By knowing the dependence of the saturated vapor pressure of the pumped gas on the temperature, in a cryopump using the described method of obtaining vacuum, it is possible to maintain the flow ratio Q 1 and Q2 (condensed, respectively, on low-temperature and high-temperature surfaces), not exceeding the ratio of the heat of evaporation of the refrigerant used to producing heat capacity of vapor used to produce heat from the vapor on the temperature difference between the refrigerant exhaust vapor and the boiling point of the latter (GN / CP (t – T0). Moreover, the required temperature of the exhaust n The aces of the refrigerant are determined with the help of a thermometer 12. The inequality sign is entered into the ratio for the reason that in any real device there are parasitic heat leads to the refrigerant vessel 2 due to radiation of warmer surrounding surfaces, thermal conductivity of the gas and suspension material, etc. ., not directly related to the condensation of the pumped gas, but nevertheless generating refrigerant vapors in vessel 2, these vapors cooling the coil 3 and the condenser with the pumped gas do useful work. The process of pumping the recipient using two cooled low-temperature and high-temperature surfaces should be continued to 760-10 Torr. When switching to the molecular mode of flow of the pumped gas, it is advisable to proceed to the condensation of the latter only on a low-temperature surface - the bottom of the vessel 2 for the refrigerant. To do this, close the valve 9 and open the valve 10, while the cryopump goes into high vacuum and ultrahigh vacuum pumping (torr and below). If it is necessary to carry out a subsequent pumping cycle of the recipient, for example, from atmospheric pressure, the sequence of operations is slightly different from the first cycle. Thus, the operation of the device according to the inventive method during cyclic pumping of the recipient makes it possible to drastically reduce the flow rate of the refrigerant liquid. Claim 1. The method of obtaining vacuum in the recipient by condensing the pumped gas on the low-temperature and high-temperature surfaces, cooled respectively by a liquid refrigerant and its vapors, characterized in that, in order to increase the economy during cyclic vacuum in the recipient, the pumped-out gas before condensation splits into two streams, one of which is condensed on a low-temperature surface, and the other on a high-temperature one, with the ratio of flow rates determined from present inequalities; Q.JQL2 (T-Tr) where ГУ, is the heat of evaporation of the refrigerant; That is the boiling temperature of the refrigerant; T-current is the maximum temperature of the high-temperature surface Cp is the heat capacity of the refrigerant vapor. 2. A device for obtaining a vacuum in the recipient, comprising a housing and a vessel with a low-temperature surface and a coil with a high-temperature surface placed in it, characterized in that the device is provided with an airtight chamber placed inside the vessel, and the coil is located with a gap relative to the inside surface of the camera and forms a closed cavity connected through a locking device with a chamber and by means of a vacuum tube with a recipient. Sources of information taken into account in the examination 1. USSR author's certificate number 545768, cl. F 04 B 37/08, 1974. 2. USSR author's certificate number 773308, cl. F 04 B 37/08, 1977.